Recently the Connected Systems Division at Microsoft has been working on some experimental public stuff that is way, way cool. From all they are working on, there is now two publicly available experimental services you'll really want to check out:
This is an open identity provider service that integrates with Cardspace to provide authentication for the other CSD services. Building a robust, secure, scalable and fully fledge STS is not trivial, and this is really good stuff.
The relay service is really exciting, as it provides a way for applications exposing services (which might be behind the firewall) to expose a public endpoint that can be accessed from outside the firewall, without the developer having to care about the network topoogy. Basically, when the service is started it registers with the Relay service to define a public endpoint through which a client can access it.
Both of these services fully integrate with the .NET 3.0 platform (particularly WCF), and they are really interesting ideas that the CSD is exploring. And there are even more of these kind of things coming down the pipeline which are even more exciting! Really recommend keeping an eye on these!
Note: Do remember this is just lab, experimental stuff. It is not production ready for now. There are no SLAs, no confidientiality, support or guarantee about them!